Reciprocating piston machines have been used to convert reciprocating motion to rotating motion, and vice-versa, and most rely on a slider-crank configuration. A conventional slider-crank mechanism includes a crank-arm that rotates about a proximal end and a distal end of the crank-arm pivotally engages (e.g., using a pin-type connection) a connecting rod at the proximal end of the connecting rod. The connecting rod pivotally engages a reciprocable slider (e.g., piston) at the distal end of the connecting rod. Consequently, as the crank-arm rotates, the slider reciprocates.
Conventional slider-crank configurations impart lateral forces to the slider that vary according to angular position of the crank and length of the connecting rod relative to the crank. For example, longer connecting rods impart correspondingly lower lateral forces compared to shorter connecting rods. Consequently, longer connecting rods usually impart lower wear rates to slider and pivoting connections. Longer connecting rods also usually result in a correspondingly lower ratio of stroke-length to overall slider-crank length, which provides a measure of the size and weight of the slider-crank mechanism relative to its useful output. To improve this measure, those of ordinary skill reduce the connecting rod length, increase the strength of pivoting connections and sliders, and either accept higher wear rates or try to reduce friction between wear surfaces (e.g., by lubricating the surfaces).
Some have attempted using planetary crankshafts and planetary gear trains for converting motion from reciprocation to rotation, and vice-versa. These prior attempts suffer from, among many issues, complex geometries that are difficult to manufacture and difficult to assemble, and high inertial forces during operation that result in low reliability and low efficiency.